1. Field of the Invention
This invention relates to a method and an apparatus for soldering a workpiece in a non-oxidizing gas atmosphere, and more particularly to a method and an apparatus for soldering a workpiece in non-oxidizing gas atmosphere with little consumption of a non-oxidizing gas.
2. Description of the Related Art
In a conventional flow soldering method, Freon has been used to wash off flux residue from a workpiece, such as a printed circuit board after the workpiece had been soldered. In order to avoid using Freon which causes atmospheric pollution, attempts have been made to eliminate this washing step from the soldering process.
One of such attempts is a process wherein soldering is performed by using a flux having a lower solid content and fewer activators than the conventional flux. However, this method causes a problem in that the lowering of the flux concentration leads to poor solderability.
After industrious investigation, the inventor of this invention found that flux residue is reduced so much that it is unnecessary to wash it off when soldering is performed in a non-oxidizing atmosphere. Based on this, he has developed an effective method and apparatus, wherein the whole soldering apparatus is enclosed by a chamber, or the solder bath is surrounded by an enclosure, and wherein non-oxidizing gas, such as N.sub.2 gas or an inert gas, is introduced into the chamber or the enclosure to form a non-oxidizing atmosphere therein.
However, the formation of the non-oxidizing atmosphere In the chamber leads to high initial and running costs. On the other hand, it is difficult to lower oxygen concentration in the non-oxidizing atmosphere in the enclosure around the solder bath, failing to obtain good solderability.
As a result of further investigation, the present inventor has arrived at the conclusion that it is sufficient to make the area where the portion of the lower surface of the workpiece and its vicinity comes out of contact with the solder flow be in a non-oxidizing state, without employing the above-mentioned chamber or enclosure, in order to solder the workpiece without the accompanying washing step.